Secondary batteries such as lithium ion secondary batteries have advantages such as high energy density, small self-discharge, excellent long-term reliability and the like, and therefore they have been put into practical use in notebook-type personal computers and mobile phones. More recently, there is a demand for development of high performance secondary batteries improved in capacity and energy density and excellent in battery performance such as cycle characteristics and storage characteristics due to the expansion of market of motor driven vehicles such as electric vehicles and hybrid vehicles and the acceleration of the development of domestic and industrial power storage systems, in addition to the trend of high functionality of electronic equipment.
Various electrolyte solutions comprising an additive are developed in order to improve battery performance, such as cycle characteristics and storage characteristics. As one example, Patent Document 1 discloses an electrolyte solution for secondary batteries comprising an aprotic solvent and a cyclic sulfonic acid ester having at least two sulfonyl groups.
On the other hand, metal type active materials such as alloys of lithium with silicon or tin and metal oxides attract attention as a negative electrode active material providing a high capacity secondary battery. These metal type negative electrode active materials provide high capacity but they have a problem that cycle characteristics decrease because expansion and contraction of the active materials are large when lithium ions are absorbed and desorbed. As a binder used for negative electrodes comprising such metal type active materials showing large expansion and contraction during charge and discharge, it is preferable to select a binder with strong binding force capable of withstanding the volume change of the active material.
For example, Patent Document 2 (Claim 1 and the like) discloses a non-aqueous electrolyte secondary battery comprising a negative electrode comprising a mixture of active material particles in which an periphery of a mixed sintered product of simple silicon and silicon oxide is covered with carbon composed of mixed composition of amorphous carbon and graphite carbon, and a thermosetting resin which undergoes a dehydration condensation reaction by heating, wherein a non-aqueous electrolyte comprises a non-aqueous solvent and at least one selected from methylene methane disulfonate, ethylene methane disulfonate and propylene methane disulfonate. The document discloses that since the thermosetting resin functioning as a binder undergoes a dehydration condensation reaction by heating and shows the effect of strongly binding active material particles, and active materials and a current collector, initial charge/discharge capacity can be improved by improvement of current collecting property due to reduction of contact resistance.
In addition, Patent Document 3 discloses that deterioration of battery properties due to the expansion of the alloy materials can be suppressed by using a negative electrode for non-aqueous electrolyte secondary batteries (Claim 1 and the like) comprising an alloy material and graphite, in which the alloy material comprises the phase A mainly comprising Si and the phase B consisting of intermetallic compound of at least one transition metal element and Si, wherein at least one of the phase A and the phase B consists of an amorphous region or a microcrystal region, the ratio of the phase A is 40% by weight or more and 95% by weight or less of the total weight of the phase A and the phase B, and the ratio of the graphite is 50% by weight or more and 95% by weight or less of the total weight of the alloy materials and the graphite. Patent Document 3 discloses that a polyacrylic acid is used as a negative electrode binder in the secondary battery.